18 Feb 2018, 17:56

Implementing the Web Share API in Your App

I was looking into how I might be able to improve the sharing experience on https://scratchthe.world, a digital scratch map PWA that I have been working. One thing I came across recently is the Web Share API, which I thought might be a strong contender for integration. The Web Share API allows for a smoother integration of sharing with popular applications on your mobile device (WhatsApp, Facebook Messenger etc). You can see the documentation on MDN here.

The cool thing about the Web Share API is it has such a minimal interface, making it easy to use an implement without complicating your code. To elaborate, it only has one method, share. The method takes an object with the properties title, text, url:

  • title refers to the title of the thing you’re trying to share, you could for example use document.title here if you’re struggling.
  • text is the text that will be shared with the link in the target application
  • url is the link itself.

Unfortunately support mobile support is not ideal; it’s missing on iOS Safari, Samsung Internet and Opera Mini as it stands.

However depending on who you trust (i.e. StatCounter which powers caniuse.com) Chrome for Android accounts for 50%+ of mobile traffic globally. That’s a lot of people that can benefit!

Another nice aspect of the Share API is it is relatively straight forward to implement a fallback, hence my choice to implement it with Scratch the World. In Scratch the World I provide a input with a link to the state of the map for people to share with there friends. If the Web Share API is available I replace that with a share button.

This isn’t the exact code I use (it is based off the Google Developers page linked above) but to give you a feel for the rough approach:

    const setupShareButton = () => {
        const shareButton = document.getElementById("share-button");

        // Add an onclick listener to the element
        shareButton.addEventListener("click", () => {
            console.log("on click");
            if (navigator.share) {
                // If we have web share enabled use that
            } else {
                // Else do something else to help people share
                // your content
    const useFallback = () => {
        console.log("Using fallback!");
        const copyPasteUrl = document.getElementById("copy-paste-url");
        copyPasteUrl.style.visibility = "visible";
        // You could add a bar with share buttons for various 
        // social media sites here as another idea
    const useWebShare = () => {
        console.log("Using Web Share!");
        // Web Share is promised based so we do .then and .catch
        // after to handle success or failure
            title: 'Using webshare!',
            text: 'This is an example of using web share',
            url: 'https://developers.google.com/web',
            .then(() => console.log('Successful share'))
            .catch((error) => console.log('Error sharing', error));


And that’s it! The more complicated bit here is coming up with a nice fallback approach. You could implement sharing workflows for common mediums like Twitter and Facebook for example. Many providers have sharing URLs that you can use to help share your content. You could combine these with Terence Eden’s SuperTinyIcons to create buttons as a performant solution. On a more experimental note, Phil Nash released a Web Component wrapper for links that will default to the Web Share API when available, which is an interesting idea.

Lastly some of you might be wondering what does the Share API look like in practice? Here’s a video of how it shapes up in Scratch the World on Android Chrome:

07 Feb 2018, 19:00

Messaging Between Tabs Using Service Worker

As of late I’ve been thinking a lot about Service Workers (sorry if this is getting boring!), predominantly in relation to the Cache API. For those of you who aren’t familiar, Service Workers are a type of Web Worker that are shared between a domain scope, and can do cool things like intercept network requests and cache them. This is powerful because it means you can improve the performance of your app for commonly accessed assets and even go offline (as the Service Worker acts a network proxy). Alongside caching, Service Workers provide a host for other capabilities for features such as Push Notifications and also syncing data in the background using the Background Sync API. Not too shabby eh?

In this post I want to think about something slightly different. As mentioned Service Workers have this interesting property in that each Service Worker is registered per scope (by default the base location of the Service Worker script). This means multiple ‘clients’ (a “document in a browser context” or more simply tabs and windows) share the same Service Worker.

One side effect of this is that these clients can pass messages to the Service Worker and then propagate down messages to other open clients. I wanted to explore the potential of this capability a little more. I did a bit of research and found this fantastic blog post from Craig Russell about sending messages with Service Workers. I want to expand on Craig’s work to take it a little bit futher into the realm of updating tab state. Under the assumption that we have correctly registered our Service Worker in the page, lets demonstrate how we might achieve basic message passing, and then see what kind of things that might allow us to do.

From the client code we need a function to allow us to post a message to a Service Worker. One misconception is that the data passed needs to be a string, but it can actually be any basic data type that is acceptable by the Structured Clone Algorithm. In short this is pretty much everything except Errors, Functions and DOM nodes. In theory if you needed to pass these things you could use JSON.stringify and JSON.parse but these present their own pitfalls. This aside let see how the message sending works:

function stateToServiceWorker(data){
    if (navigator.serviceWorker && navigator.serviceWorker.controller) {

So this function covers sending from the client, what about receiving from the client? We could do something like this in our registration code to register for messages from our Service Worker:

if ('serviceWorker' in navigator) {

        .then(function() {
            return navigator.serviceWorker.ready;
        .then(function(reg) {
            // Here we add the event listener for receiving messages
            navigator.serviceWorker.addEventListener('message', function(event){

        }).catch(function(error) {
            console.error('Service Worker registration error : ', error);


This concludes our client side code for sending and receiving messages. Now what about our Service Worker? Firstly lets examine receiving messages:

self.addEventListener('message', function(event){
    // Receive the data from the client
    var data = event.data;

    // The unique ID of the tab
    var clientId = event.source.id 

    // A function that handles the message
    self.syncTabState(data, clientId);

Now that we’ve received a message from the client, we need to know how to send it back to potential clients. We could probably inline this code but wanted to break it down for this demonstration:

self.sendTabState = function(client, data){
    // Post data to a specific client

Greg’s post actually shows how you can send a message back to the client in question if you so wish. This can be done by sending a reference to a MessageChannels ports across and using some nice Promise callback wrapping, but for the sake of simplicity I’m omitting that here.

Now we can send some message to any specific client of our choosing, but how do actually call this function to access all the clients? We could do something like this:

self.syncTabState = function(data, clientId){
    clients.matchAll().then(function(clients) {

        // Loop over all available clients
        clients.forEach(function(client) {

            // No need to update the tab that 
            // sent the data
            if (client.id !== clientId) {
                self.sendTabState(client, data)

So we’ve shown how to send and receive messages from the Service Worker. What’s the actual use case for this? Well the original idea I had in mind was quite abstract in syncing state across all opened tabs for an application. Let me show you a basic example through the medium of the this suboptimal gif:

Since then I’ve had a deeper think and I believe there might be some more exact/substantial use cases for this technique to consider, especially in the web app space. For example you could sync the state of your application across tabs without the explicit need for polling/websockets, or watching localStorage / IndexDB. Think updating a balance after bank transfer on another tab, or close a EU cookies banner simultaneously across open clients. You could also do things like triggering tabs that are on a specific route to perform some action, like open a specific dialog or hide information that is no longer relevant. Kitson Kelly made the point that this could come into it’s own in more heavy weight / power-user centered applications.

I’d be really opening to hearing other peoples suggestions on the matter, so feel free to drop me a line on Twitter. If you are interested in seeing the code you can check out the GitHub here.

24 Dec 2017, 14:53

Getting going with ES6 Maps

As we move into a world where modern browsers are supporting the nearly the entire ES6 specification, we have a variety of data structures to use for storing and accessing our data as native built-in primitives. In ES6 we specifically gain access to ‘keyed collections’. Keyed collections encompasses four built-ins, these are namely Set, Map, WeakSet and WeakMap. Here we’ll be talking about the Map in particular. Let’s get stuck in!

What is a Map?

A Map is a collection of key value pairs, where both key and values can be of any type. This differs from how one might have traditionally used a JavaScript Object as a map, as historically keys have been strings only (this has changed with the introduction of Symbols but that’s for a different blog post to come!).

const obj = { 1 : "one" }
typeof Object.keys(obj)[0] // Evaluates to string

So with Maps, we have the additional power of using anything we like as our key, even a HTMLElement, which is powerful because it makes it easy to associate data with a DOM node. To illustrate the use of none String keys, we can see this example using booleans:

const map = new Map([
    [true, "Things that are true"],
    [false, "Things that are false"]

Here true and false are the respective keys in our collection. So how does JavaScript know how to evaluate something as matching a Map key? Well the approach is very similar to the === (identity) operator, with the minor caveat that NaN (Not a Number) equates to NaN even though NaN !== NaN.

How do we use it?

Maps provide a set of methods for interfacing with them such as get, set and delete. These methods provide a clean inteface for interacting with our data. Let’s see how that works in practice:

const one = "one";
const map = new Map([ ["one", 1] ])
map.get("one"); // Returns 1
map.get(one); // Returns 1

map.set("two", 2);
// Returns the Map with "two" set to 2

// Returns true if successful or false if unsuccessful

// Returns undefined

As you can see there’s a little gotcha here, get, set and delete all have different return behaviours. Get will return the associated value, set will return the Map itself, and delete will return a boolean, and clear returns undefined. Something to keep in mind!

We also have some really nice convenience methods to help us interface. For example, has which will tell us if a key exists in a Map:

const map = new Map([ ["one", 1], ["two", 2] ]);
map.has("two") // true

This is very useful for quickly checking the existence of key in a Map. What about if we want to iterate over a Maps contents? Firstly there are a few convenient methods in this regard: values, entries and forEach. Let’s look at values and keys. Both these methods return an iterable. Iterables are a little outside the scope of this post, but think of them as JavaScript variables that have defined behaviours for what happens when you iterate over them (for example using for…of):

// Entries
const map = new Map([ ["one", 1], ["two", 2] ]);

for (const num of map.entries()) {
    // Logs ["one", 1]
    // Then ["two", 2]

// Values
for (const key of map.values()) {
    // Logs 1
    // Then 2

Alongside this we have the forEach method that some of you may be familiar with from the Array method of the same name. It behaves like so:

const map = new Map([ ["one", 1], ["two", 2] ]);
map.forEach((key, value) => console.log(key, value));
// Logs ["one", 1]
// Then ["two", 2]

Lastly we can quickly and conveniently get the size of a map with the size method. It is fairly straight forward and operates like so:

const pets = Map([ ["dog", "woof!"], ["cat", "meow"], ["goldfish", "bop bop bop"] ]);
animals.size(); // Evaluates to 3

Which would have been less elegant using an Object:

var pets = {"dog", "woof!", "cat": "meow", "goldfish": "bop bop bop"};

Why use a Map?

Simply put, the Map is more idiomatic and effective primitive than an Object for use as a mutable key-value pair data structure. We have the added flexibility of using anything we please as our keys, alongside a clear set of a powerful methods that we have shown above. These methods allow us to be more semantic and straightforward about interacting and manipulating our data. It also avoids some of the potential pitfalls of the Object, for example, because of the interface of a Map, we can avoid the possibility of colliding with default Object properties such as toString or hasOwnProperty. This is obviously an edge case but provides us with extra reassurance:

// With a traditional Object
const obj = {};
obj["toString"] = "woops";
// Evaluates to woops

// With a Map
const map = Map();
map.get("toString") // undefined
map.set("toString", "This is fine");

Overall it expresses a lot of cool properties that suite it better to behaviours we wanted from using an Object as a Map previously. Happy Mapping!